aura-mus: Implement DesktopWindowTreeHostMus::StackAbove().

services/ui/ws/default_access_policy.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SERVICES_UI_WS_DEFAULT_ACCESS_POLICY_H_
 #define SERVICES_UI_WS_DEFAULT_ACCESS_POLICY_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 35 matching lines @@
       const ServerWindow* window) const override;
   bool CanSetWindowBounds(const ServerWindow* window) const override;
   bool CanSetWindowProperties(const ServerWindow* window) const override;
   bool CanSetWindowTextInputState(const ServerWindow* window) const override;
   bool CanSetCapture(const ServerWindow* window) const override;
   bool CanSetFocus(const ServerWindow* window) const override;
   bool CanSetClientArea(const ServerWindow* window) const override;
   bool CanSetHitTestMask(const ServerWindow* window) const override;
   bool CanSetAcceptDrops(const ServerWindow* window) const override;
   bool CanSetAcceptEvents(const ServerWindow* window) const override;
+  bool CanStackAbove(const ServerWindow* above,
+                     const ServerWindow* below) const override;
   bool CanStackAtTop(const ServerWindow* window) const override;
   bool CanSetCursorProperties(const ServerWindow* window) const override;
   bool CanInitiateDragLoop(const ServerWindow* window) const override;
   bool CanInitiateMoveLoop(const ServerWindow* window) const override;
   bool ShouldNotifyOnHierarchyChange(
       const ServerWindow* window,
       const ServerWindow** new_parent,
       const ServerWindow** old_parent) const override;
   const ServerWindow* GetWindowForFocusChange(
       const ServerWindow* focused) override;
   bool CanSetWindowManager() const override;
   bool IsValidIdForNewWindow(const ClientWindowId& id) const override;
 
  private:
   bool WasCreatedByThisClient(const ServerWindow* window) const;
 
   ClientSpecificId client_id_ = 0u;
   AccessPolicyDelegate* delegate_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(DefaultAccessPolicy);
 };
 
 }  // namespace ws
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_DEFAULT_ACCESS_POLICY_H_